<?php

$funArr = ['add','sub','mul','div'];

$randKey = array_rand($funArr);
echo $funArr[$randKey];
echo $funArr[$randKey](24,6);

function add($a=0,$b=0){
  return $a+$b;
}
function sub($a=0,$b=0){
  return $a-$b;
}
function mul($a=0,$b=1){
  return $a*$b;
}
function div($a=0,$b=1){
  return $a/$b;
}
